The present invention relates to an electronic still camera which picks up images with use of a solid image-pickup device and particularly to an electronic still camera which shortens the release time lag.
Widely spreading now are so-called electronic still cameras in which an object image is formed on, for example, a CCD two-dimensional image sensor by an image pickup optical system and is converted into an electric signal, and the image signal of a still image thus obtained is recorded on a recording medium such as a semiconductor memory or a magnetic disk.
This kind of electronic still camera generally takes a quite longer time from when the power is turned on to when operation can be transferred to image pickup or from when a button is operated to when image pickup action can be actually taken while the power is on than a camera using a silver film. The latter time is a so-called release time lag. Electronic still cameras are said to be weak in chances for good pictures because of the long release time lag.
Even in an electronic still camera as described above, it is possible to shorten the release time lag if a stand-by current is constantly kept flowing through the image pickup device and if preliminary operations for image pickup, e.g., automatic exposure, white balance adjustment, and automatic focus adjustment are constantly carried out at a high frequency.
However, in electronic still cameras, the capacity of a battery as a power source which electrically enables all the operations is limited. Consequently, preliminary operations for electric conductance of a stand-by current as described above or image pickup, which shorten the release time lag, are carried out thoughtlessly, the electric power is consumed wastefully and the battery lifetime is shortened greatly.